This invention generally relates to an apparatus for detecting and measuring low frequency pulsed/alternating magnetic fields to which a person may be exposed, and which may create a health hazard at high or continued exposure levels. More particularly, the invention relates to a magnetic and electric field radiation monitor which is compact and easily used to allow the device to be easily carried to various locations and environments in which a person may be exposed to such radiation. The monitor allows the detection and the measurement of magnetic and electric fields emitted from various electronic equipment and the like, such that the location and strength of the fields may be determined to allow reduction of personal exposure to such fields.
Recently, the effects of pulsed/alternating magnetic fields emitted from such things as video display terminals (VDT's), television receivers, microwave ovens, power lines or a variety of other devices which emit pulsed/alternating magnetic fields, have been linked to increased health risks for persons exposed to such fields. The potentially harmful health effects of electromagnetic emissions from this various electronic equipment include an increased risk of developing cancer, risks of birth defects and miscarriages in pregnant women, and other health hazards. The evidence of such health risks has been increasing dramatically within the last few years, and recognition of the problem is slowly being acknowledged within the industry and community. The epidemiological evidence being gathered on the hazardous effects of electromagnetic fields given off by various electronic equipment has been mounting. This evidence has led to various responses initiated by manufacturers of equipment emitting potentially harmful electromagnetic radiation, as well as by governmental authorities who have imposed restrictions upon emissions from various equipment to minimize the risk posed thereby. Various editorials and articles provide general background information on the potential risks of the low frequency pulsed/alternating magnetic fields emitted from various electronic equipment, such as found in MACWORLD, July 1990 issue at page 136, POPULAR MECHANICS, November 1990 issue at page 110 as well as others. Although these articles have raised the public awareness about the possible dangers of low frequency electromagnetic fields or radiation, the industry has not yet responded in an adequate fashion to provide individual protection to the user of such equipment.
The magnetic fields which are deemed a potential health hazard are normally generated from power lines and other high-voltage electrical apparatus, which emit extremely low frequency (ELF) magnetic fields in the 50-1000 Hz range, as well as the higher frequencies termed very low frequency (VLF) emissions in the range of 10-500 KHz. As an example, the ELF magnetic fields emitted by video display monitors were tested as described in the MACWORLD article mentioned hereinbefore, magnetic field emissions were measured at various distances from all portions of various monitors. It was found that the strongest emissions from video display terminals are at the sides and tops of the monitors, wherein the field strength may be as much as 70 milligauss (mG) at a distance of 4" from these areas. Field strengths at the front of the VDT were over 22 mG at the same distance, but at a longer distance such as 28" from the front of the VDT, the emissions dropped to below 1 mG. Although this generalized information would indicate that keeping a safe distance from a VDT or other electromagnetic radiator may minimize the harm of such fields, for any particular environment in which a person may be placed, the exact location and field strength of magnetic field radiation may not be generally surmised. It is also noted that the magnetic field radiation from such electromagnetic radiators may not be shielded by simple shielding structures, and therefore other means must be utilized to minimize emissions from such equipment. Various attempts have been suggested for minimizing the actual emission of pulsed/alternating magnetic fields from such devices, such as a compensating coil placed in a VDT or the like which produces lines of magnetic flux moving in opposition to those generated from the CRT's deflection coil. Also, LCD or electroluminescent displays have been found to emit negligible magnetic fields, and may be resorted to minimize emissions, but such equipment is higher in cost and does not provide similar performance characteristics as CRT technology.
Although the approach of minimizing the emissions from such equipment will be a necessary step to minimize the risk associated with use of such equipment, there is a critical need to provide an individual with the ability to monitor and measure possible emissions of magnetic field radiation so that they themselves may minimize the potential risk of exposure to such fields by positioning themselves to eliminate or minimize such exposure Various types of electromagnetic field measurement apparatus are available, for example, a VDT/VLF Radiation Survey Meter Model HI-3603, which is stated to measure electromagnetic field strengths in the frequency range from 10 KHz to 300 KHz, and an ELF/Power Frequency EMF Survey Meter Model HI-3604 designed to evaluate electric and magnetic fields associated with 50/60 Hz power lines and the like, both manufactured by Holaday Industries, Inc. Another apparatus for electromagnetic field radiation measurement is a digital display field monitor model ELF-50D produced by Walker Scientific Inc., which is a portable, hand-held instrument designed and calibrated to measure low level 50 Hz or 60 Hz electromagnetic field radiation. These and other companies also produce a variety of other gaussmeters, magnetometers and fluxmeters for magnetic field measurement in a variety of different applications including nuclear magnetic resonance applications and other industrial applications.
Generally, these types of instruments as manufactured by these and other companies are designed as laboratory or industrial measurement tools rather than for use by the general public. Such equipment is limited in its application for use by the general consumer as the cost of such instruments are high and therefore impractical and generally unavailable to the individual. Additionally, many of these devices are operationally complex, and again generally unusable by the individual. Various other lower cost devices have been introduced, such as the Walker Scientific Model ELF-50D, which is a portable, hand-held unit and of lower cost, but which is calibrated for a fundamental frequency only and therefore limited to a single frequency response. Any devices of similar type generally suffer from limited or single frequency response, which will prevent the user from achieving a complete or accurate measurement of magnetic fields of a complex nature typically emitted from video display terminals, television receivers and the like. Additionally, such instruments are again difficult in their use to obtain accurate and valid quantitative measurements of magnetic field radiation. Similarly, electric field measurements are desirable in many situations, and accurate field measurements have not been generally achievable with a low cost, easily used device.